Abstract
Inactivated Sendai virus (hemagglutinating virus of Japan; HVJ) envelope (HVJ-E) induces anticancer immunity and cancer cell-selective apoptosis through the recognition of viral RNA genome fragments by retinoic acid-inducible gene-I (RIG-I). Here, we discovered that the "copy-back" type of defective-interfering (DI) particles that exist in the Cantell strain of HVJ induced the human PC3 prostate cancer cell death more effectively than the Sendai/52 strain or Cantell strain, which contain fewer DI particles. DI particle genomic RNA (~550 bases) activated proapoptotic genes such as Noxa and/or TNF-related apoptosis-inducing ligand (TRAIL) in human prostate cancer cells to induce cancer cell-selective apoptosis. DI particle-derived RNA was synthesized by in vitro transcription (in vitro transcribed (IVT)-B2). IVT-B2 RNA, which has a double-stranded region in its secondary structure, promoted a stronger anticancer effect than IVT-HN RNA, which does not have a double-stranded region in its secondary structure. The intratumoral transfection of IVT-B2 significantly reduced the volume of a human prostate tumor and induced tumor cell apoptosis in the xenograft mouse model. Moreover, the involvement of natural killer (NK) cells in IVT-B2-RNA-induced anticancer effects was also suggested. These findings provide a novel nucleic acid medicine for the treatment of cancer.